Numerous materials and methods have been developed to provide spatial and temporal control of the delivery of cells and drugs for localized therapy. For example, in cancer management, nanoparticles derived from either synthetic materials or natural materials can be used as vehicles to carry therapeutic drugs, genes, and imaging agents [Reference 1 below]. The nanoparticles are usually “decorated” with targeting ligands or molecules such as peptides, antibodies, aptamers, and proteins that are specific to the receptors expressed or overexpressed on the cancer cells [References 2, 3]. Such payload-bearing nanoparticles are called “stealthy vehicles” or “Trojan horses” as they can be injected into the circulation and accumulate into the tumors through a passive targeting mechanism, namely enhanced permeation and retention (EPR) caused by the leaky vasculature and the malfunctioned lymphatic drainage in tumors, and/or an active targeting mechanism via the guidance of cancer-specific ligands or molecules [References 4, 5]. Unfortunately, despite significant progress in the discovery of surface markers, targeting ligands and molecules, and biomaterial carriers, very few nanoparticles are truly specific after intravenous injection, and the targeting remains essentially chance-dependent, which results in a wide bio-distribution of nanoparticles (and their payloads) throughout the body, thus causing significant side effects [References 2, 6, 7]. Realizing truly specific “live” or “smart” targeting for effective drug delivery in cancer management remains a significant challenge.